The invention relates to an endless paper web folded in a stack and for feeding the paper web to the printing unit of a high-speed printer, particularly a laser printer applying a removal force and with paper web guide and removal rollers, whereof at least one is driven.
In printers for large computers and the like, namely laser printers, working takes place with a considerable working speed predetermined by the computer. The printer has paper stack shafts, in which can be placed the endless paper to be printed and located in cartons and is then threaded into the actual printing unit by a printer or supply shaft. The stacks are placed in cases in such a way that each individual sheet to be printed is defined by perforations and, in this manner, separably connected to the next sheet, with the individual sheets being directly superimposed in zig-zag manner and each perforation being folded over. As such computer paper stacks are transported by hand and must, in particular be manually transferred from a pallet to the printer, the stacks can only have a certain weight and, consequently, only a certain number of paper layers. The capacity of the high-speed printer can, consequently, not be fully utilized, because in the case of such printers it is necessary after a short time period to insert a new paper stack, which has to be threaded into the printing unit. This leads to long laser printer down times preventing a complete utilization of the printing speed of the printer and the capacity thereof. Attempts have been made to replace the preperforated paper stacks by rolls, but the latter are very heavy and voluminous, so that they generally require a completely different mounting support arrangement and transport conditions. A further disadvantage is that as a result of the lack of prefolding, the forms can no longer be easily placed in a stack and instead must be separated by tear-off or cutting equipment. The possible paper roll slope caused by the rolling up of the paper web may lead to difficulties in this case. Furthermore, during rolling up, the printing ink printed on the forms is sealed in a relatively air-tight manner, so that a completely satisfactory drying of the print is not ensured. During the burn-in process performed at high temperatures in connection with laser printers, this can lead to the evaporation of ink constituents and, consequently, to undesired contamination effects at the burn-in station. Ultimately a considerable amount of technical effort and expenditure is required for the roll suspension and movement upstream of the high-speed printer, as well as for the necessary tear-off or cutting equipment.
It has already been proposed to leave several, e.g. two raiseable "small stacks" in their cartons on a support plate and which are insertable in the printer shaft, whereby a device provided in addition to the printer and arranged on a base plate and after removing the door closing the printer paper stack shaft can be partly inserted into the latter, whereby the paper web is removed from the stacks and introduced into the printer. Admittedly the individual small stacks no longer have to be raised into the printer shaft, but through the use of such small stacks the capacity continues to be limited, because the device has only a limited height, so that higher stacks cannot be inserted. Quite apart from the fact that the removal process has to be continuously monitored by somebody or, if this is not done, the paper web is drawn into the paper shaft, and it is only possible to establish therein the paper web end by a detector arrangement, so that the connection with the next web can only take place in a complicated manner, it is a considerable disadvantage of the known device that the stack shaft door provided for noise reduction purposes cannot be closed. Thus, operation leads to a considerable noise level. Furthermore, although in the known device driven rollers are provided, they must also be stopped at least in the case of a prolonged shutdown of the printer, because as a result of the guidance of the paper web over at least one of the driven rollers, there would otherwise be an undesired paper accumulation through the further conveying of the paper in the vicinity of the driven rollers, but lack of a continuing removal in the printer, which can lead to a displacement of the web in the deflection zone and to faults. A further disadvantage is that, as the complete device is partly inserted in the printer shaft on a common base plate, the same is no longer accessible for enabling, for example, changing the printing paper and, for example, direct printing from the paper stack shaft. Thus, the known device suffers from lack of flexibility and a large number of disadvantages, quite apart from the fact that at the best it can be used in a single known printer type, namely the IBM 3800, but not in other printers and due to the inflexibility, can hardly be used in future high-speed printers.
The invention is based on the aforementioned apparatus and sets the problem of providing an apparatus which, while avoiding the aforementioned disadvantages, flexibly has numerous possible uses and combinations with different printers, while considerably reducing noise. In addition, the tensile forces acting on the paper web are reduced and an undesired tearing of the paper web prevented.
In an apparatus of the aforementioned type, this problem is solved in that the paper web is guided below the driven roller, with the driven roller having its own drive and being continuously driven, even when the printer is stationary. A roller deflecting the paper web in the horizontal direction of travel is arranged directly behind the paper stack in its lower zone above the punching base, with the paper web being introduced into the printer with a horizontal transverse extension. At least one intake roller is arranged above the punching base and introduces the web into the printer and the deflection roller provided in the vicinity of the stack has a variable relative spacing.
As a result of the inventive construction, the aforementioned disadvantages of the known apparatus are avoided, because the removal and introduction units of the inventive apparatus are spatially variable, so that the complete apparatus can be used in the most varied way with respect to the printer, without it being necessary to accept other disadvantages. In particular, as a result of the horizontal orientation of the paper web, a noise reduction can be achieved at least on introducing into the printer, either below the lower edge of a sidewall of a printer standing on feet, or through a door slot below the door of a printer or in some other way. As a result of the inventive construction the removal drive arranged on the high-speed printer is given a supporting drive in the vicinity of the paper web travel distance, so that, in the case of a corresponding matching of the drive, the removal force can be applied over a shorter distance, so that the paper web is less stressed A separate drive motor can be provided for the driven deflection roller. Advantageously the driven deflection roller rotates continuously, so that even if the printer is stopped and a removal force is no longer exerted, it still conveys the paper web by a short distance, without there being a large paper web accumulation. When the printer is stationary, due to its guidance, the paper web is directly raised from the same or "drops from it", so that the adhesion between paper web and deflection roller is very rapidly lost and the latter rotates freely.
The continuous deflection roller drive also has the advantage on starting the printer, that at the instant when the paper web is tensioned again, the deflection roller again assumes its supporting drive function. Thus, the removal force acting intermittently on starting is only transferred to the paper web portion located between the printer and the driven deflection roller, while being damped by the gradual application of the paper web to said roller until finally the necessary transfer friction is obtained and it is not transferred into the further paper web. The choice of deflection rollers, which are provided with a drive, will be decided as a function of the particular circumstances, but a driven deflection roller should be positioned in the vicinity of the high-speed printer paper shaft.
In many applications, the paper web removal direction from the large stack differs from the infeed direction into the high-speed printer, so that it is necessary to provide a turning cross, which e.g. optionally comprises an intake roller arranged at right angles to the removal direction, a turning bar positioned immediately behind it and set at an angle smaller than 90.degree. with respect thereto and a further discharge roller arranged at right angles to the infeed direction. Within the turning cross, the turning bar makes it possible to deflect the paper web at right angles to its travel direction e.g. by 90.degree., while it can also be deflected by the discharge roller in the direction of its extension. According to the invention, when such a turning cross is used, the discharge roller of said turning cross is driven.
The turning cross is generally located directly upstream of the high-speed printer, if e.g. the palletized large stacks are to be set alongside said printer. As a result of the deflection, particularly high frictional forces act on the paper web in the vicinity of the turning cross, so that the risk of tearing is correspondingly high at this point. The arrangement of at least on driven roller in the vicinity of the turning cross, preferably the discharge roller consequently has a particularly advantageous effect at this point.
In order to very effectively transfer the driving force from the driven roller to the paper web, according to a preferred embodiment a guide roller is associated with the driven roller at a limited parallel spacing and the paper web is initially guided over the driven roller and then over the guide roller, while modifying the travel direction between the rollers.
Thus, the paper web is guided between the driven roller and the guide roller in a loop, so that the looping angle necessary for transferring the driving power from the driven roller to the paper web is ensured.
A complicated controlled drive is rendered unnecessary as a result of the continuous feed effect. It is therefore possible to deal with large stacks, as had been proposed in connection with the basic idea of a removal mechanism, but where it was disadvantageously provided for the paper web to be guided through the base, i.e. structural changes where required and in the present case no problems occur in the removal area. Through the drive of the web outside the printer, there is a tensionless transfer, particularly directly over the base, the web optionally being covered. The paper stack shaft and the complete operating side of the printer can be left free, because they do not have to be adjusted by a removal mechanism arranged very close thereto. The operation of the printer is freely ensured.